This invention relates to an improved process for crimping tows of wet fibers. The process is particularly useful in the crimping of wet tows comprised of acrylic fibers.
In the crimping of tows of wet fibers following processing in one or more aqueous baths, it is customary to remove some of the water from the tow by squeezing the tow under moderate pressure, e.g., 35 lbs./in., whereby the moisture content of the tow is reduced to 60 to 90% by weight. Finish is then applied to the tow and the tow is crimped, e.g., in a stuffing box crimper whereby finish and solvent-containing water are exuded from the tow. Although the exudate consists mostly of water derived from the finish and the aqueous baths, it cannot be simply discarded because of pollution considerations. The exudate cannot be returned to the bath for ultimate recovery of solvent because the finish causes excessive foaming in the bath. Recovery of solvent from the exudate is difficult because breakdown of finish components cause fouling of the distillation equipment used in solvent recovery. If the exudate is reapplied to the tow in the stuffing box, the crimp tow contains excessive water and solvent. If such a tow is lagged in cans before drying, as is the usual practice, the excessive moisture tends to separate toward the bottom of the can. When tow from such cans is passed through a dryer, uneven drying results causing non-uniformities in the tow. It would be highly desirable to avoid both the necessity of recovering solvent from the exudate and the loss of finish.
The present invention provides an improved process for crimping tows of wet fibers whereby essentially all of the applied finish is retained on the fibers. Consequently, no pollution with respect to finish occurs.
This invention provides an improved process for crimping an advancing tow of fibers which have been processed in an aqueous bath or series of aqueous baths wherein the tow is uniformly compressed in a confined space under a nip pressure of 600-1,000 lbs./in. to exude solvent-containing water from the tow, the exudate being returned to the last aqueous bath, a predetermined amount of finish is applied to the tow, the fibers are crimped in a stuffing-box crimper whereby some of the finish and a small amount of residual moisture are exuded from the tow, the exudate is recovered and removed to a storage container, the exudate is reapplied to the tow in the stuffing box at a rate corresponding to the rate of expression and the crimped tow is collected and then dried. Preferably, the tow is comprised of acrylic fibers and the tow is compressed to contain 25-35%, preferably 30-35% by weight water. Most preferably, the nip pressure is about 800 lbs./in.
In conventional processes wherein a tow of fibers is treated in an aqueous bath or a series of aqueous baths, finish is usually applied to the tow immediately upon removal of the tow from squeeze rolls following the last aqueous bath. An example of such tow processing occurs in the wet or dry spinning of acrylic fibers wherein the freshly spun fibers are extracted to remove spinning solvent and drawn while passing through a series of hot aqueous baths with countercurrent flow of the bath liquid from one bath to the preceding bath. The liquid from the first bath is removed for recovery of the spinning solvent, usually by distillation. The squeeze rolls are operated under a moderate pressure, e.g., 35 lbs./in. whereby the water content of the tow is reduced to about 60 to 90% by weight.
According to the present invention, the finish is not applied to the tow leaving the squeeze rolls but rather the tow is passed to precision squeeze rolls preferably comprised of a smooth flat roll and a matching flanged roll designed to provide a positive nip area through which the tow passes. These rolls should be capable of exerting a force in the range of 600-1,000 lbs./in. Solvent-containing water which is squeezed out of the tow by these rolls is returned to the last aqueous bath for eventual recovery of the solvent. These rolls can replace the pull rolls normally used to feed a stuffing-box crimper. Finish is applied to the tow and the tow is fed into a stuffing-box crimper where some of the finish and a small additional amount of solvent-containing water is exuded from the tow. This exudate is collected and re-applied to the tow at the same rate as it is exuded. The crimped tow is collected and dried. Tows crimped according to the process of the invention have a lower content of moisture than prior art tows and thus can be dried more easily.